I. Field of the Invention
This invention relates to apparatus for cleaning or finishing the surface of articles by directing a more pressurized flow of a cleaning media against the article surface and, in one aspect, to abrasive blast cabinets capable of using a fine powder abrasive blast media for that purpose.
II. Description of the Prior Art
Abrasive blast cabinets typically include a blast compartment or chamber in which the article or articles to be cleaned or polished by an abrasive blasting material are placed. The operator usually reaches through arm holes protected by rubber gloves and, observing through a front window in the blast chamber, either picks up an article to be cleaned and moves it under a stationary blast nozzle or picks up a portable blast nozzle and moves it about to direct a high velocity jet stream of the abrasive material over the surfaces of the article.
Abrasive blast cabinets typically are either a suction or pressure type. In suction-type blast cabinets, a stream of pressurized gas flows through in an air jet in a blast gun and creates a vacuum condition which causes the blast media to be aspirated from a source and mixed with the air stream. A high velocity, abrasive media-containing air stream is discharged from the nozzle. In the pressure-type blast cabinet, a flow of compressed air passing through or in communication with a blast media in a storage tank or the like picks up the media and the resulting abrasive media-containing air stream is directed to the blast nozzle. Examples of prior construction for abrasive blast cabinets are disclosed in U.S. Sheesley et al. Pat. No. 4,505,077 and U.S. Klaas Pat. No. 4,579,570.
The blast media typically used with either type blast cabinet is a relatively hard particulate material, such as chilled iron grit or aluminum oxide, which normally experiences a limited break down during use and is recycled for use after removing contaminants.
Fine powder abrasive materials, such as sodium bicarbonate-based materials, are preferred for some applications because they are less harsh to the surface being cleaned, are nonhazardous to persons operating or working in the vicinity of blast cabinets and the disposal of the spent media is greatly simplified. Dry forms of this type of material generally cannot be used as a blast media in conventional blast cabinets because the material is friable and breaks down into dust-like particles which are dispersed throughout the blast cabinet and produce a dense, fog-like condition. This condition cannot be eliminated or adequately reduced by conventional blast cabinet ventilation technology. Consequently, the operator most often is unable to observe the article being cleaned. This is particularly true for operations using higher velocity jet streams.
A similar problem can exist for other cleaning operations employing a finely atomized liquid cleaning media or other cleaning media which tends to disperse in a manner to obscure visibility in the area surrounding the article being cleaned.